A Closer Look at the Alpha Persei Coronal Conundrum

Abstract

A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found far-ultraviolet coronal proxy Si IV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multi-faceted program tested that premise. Groundbased optical coronography, and near-UV imaging with HST Wide Field Camera 3, searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si IV emissions of α Per, in a deeper FUV spectrum collected by HST COS as part of the joint program, aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution -a well separated companion -has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.Subject headings: ultraviolet: stars -stars: individual (HD 20902= α Per; HD 45348= α Car) -stars: coronae Ignoring these caveats for the moment, the suspicious ROSAT offset, bolstered by the 1 In what follows, "α Per" normally will refer to the star, while "Alpha Per" normally will denote the cluster. In cases where "Alpha Persei" appears, the specific usage is guided by the context.2 Brief, partial-orbit observations to fill gaps in the HST schedule.3 Position Sensitive Proportional Counter, the main X-ray imager of ROSAT.

The UV Emission of Stars in the LAMOST Survey. I. Catalogs

“…The star has strong emission lines in the FUV that are unpredicted by the model. It may have a white dwarf companion, but there is still no solid evidence (Ayres 2017 The survey has obtained more than four million spectra of stars from October 2011 to May 2015 (Section 2). The spectral types of these stars and accurate estimation of the stellar parameters are produced by the LAMOST standard data processing pipeline (Luo et al 2015).…”

Refined fundamental parameters of Canopus from combined near-IR interferometry and spectral energy distribution

“…Canopus presents high energy emission in the UV and X-ray, the physical origin of which is not completely understood: (i) a magnetic field of several hundred gauss, measured from Zeeman shifts on UV spectral lines, associated with periodic variations of a few days to a few weeks (e.g., Weiss 1986;Rakos et al 1977;Bychkov et al 2005Bychkov et al , 2009; (ii) far-UV emission lines showing non-symmetrical bisector curves with reverse C-shapes, revealing the present of opacity effects and/or velocity fields Dupree et al (2005); and (iii) a high X-ray luminosity L X of a few 10 30 erg s −1 (e.g., Vaiana et al 1981;Strassmeier et al 1998;Hunsch et al 1998;Testa et al 2004;Ayres 2011Ayres , 2017Ayres , 2018.…”

Prospects for X-Ray and FUV Observations to Provide Insight Into the “Cepheid Mass Problem”

“…However, when Cepheids are placed within the broader context of cool supergiants, X-ray activity may be more common than originally thought. Recent studies (Ayres, 2017(Ayres, , 2018 have shown that a number of non-pulsating, cool supergiants also display FUV emission lines and X-ray activity. Using ratios of FUV/X-ray to bolometric luminosity, the studies show that Cepheids behave similarly to their non-pulsating counterparts, and stand apart from cool dwarf stars.…”